With the ever-growing needs for wireless communications, much more efforts to provide a fully integrated radio frequency (RF) transceiver have been made in order to achieve lighter bill of materials, smaller form factor, and more functionality. To meet the requirements of wireless systems, power amplifiers (PAs) using Complementary Metal-Oxide-Semiconductor (CMOS) technology is a good candidate, and higher level of transceiver integration including PA has recently been demonstrated for some wireless communications such as wireless LAN, Bluetooth, and Cordless phone. However, fully integrating a power amplifier on silicon or silicon based wafer still presents a variety of difficulties. In particular, two major issues in the design of fully-integrated high-speed solid state power amplifiers using CMOS are (1) the low breakdown voltage of the transistors, and (2) the lossy substrate on which the performance of the passive components such as inductors and transformers is degraded.
Due to these and other drawbacks, there is an opportunity for simultaneous power combining and impedance transformation by transformer-type output networks. Likewise, there is an opportunity for multi-primary and distributed secondary transformers for power amplifier systems.